Rates of PTSD among Veterans (e.g.,13.5% among returning Veterans; Dursa, Reinhard, Barth, & Schneiderman, 2014) are disproportionately high relative to those who have not served in the military (3.5%; Kessler et al., 2005). Compared with those without the disorder, individuals who suffer from PTSD have higher rates of additional negative outcomes, including impaired quality of life (Schnurr, Lunney, Bovin, & Marx, 2009), and more psychological (Kessler et al., 2005) and physical (Schnurr, 2015) comorbid conditions. The high PTSD prevalence among Veterans and the associated consequences highlight the importance of effective screening efforts. The goal of PTSD screening is to identify trauma-exposed individuals with probable undiagnosed PTSD in order to intervene earlier in the course of disease. To that end, the Department of Veterans Affairs (VA) has mandated that all Veterans be screened for PTSD annually for the first five years after military separation and every five years thereafter, unless the Veteran has had a PTSD diagnosis entered in his/her medical record in the past year (Vista Clinical Reminder User Manual, 2007). Because an estimated 90% of patients who have received mental health diagnoses are seen in primary care settings (Gebhart & Neeley, 1996), all Veterans seeking care at VA primary care clinics are routinely screened by their clinician. Currently, VA uses the Primary Care PTSD screen (PC-PTSD) to identify Veterans with probable PTSD. This 4-item questionnaire is based on the PTSD diagnostic criteria included in the fourth edition of the Diagnostic and Statistical Manual of Mental Disorders (DSM-IV) of the American Psychiatric Association (APA, 1994). In 2013, the APA introduced the DSM-5, which included a number of significant revisions to the PTSD diagnosis. In response, the PC-PTSD was updated to add (1) a trauma-specific stem that reflects changes made to PTSD Criterion A and (2) a new item that reflects the revisions made to the PTSD symptom criteria in DSM-5. The new instrument, the PC-PTSD-5, therefore better reflects the new knowledge the field possesses about PTSD. Despite revisions to the PTSD diagnosis as well as the PC-PTSD to reflect those changes, VA continues to use the old version of the measure until a valid cutoff for the PC-PTSD-5 is established. Although initial pilot data for the PC-PTSD-5 indicate it is psychometrically sound, it has not yet been compared with a gold standard PTSD diagnostic interview, such as the Clinician Administered PTSD Scale for DSM-5 (CAPS-5), in a VA primary care setting. The proposed project will identify a valid cutoff for the PC-PTSD-5 using a primary care sample with the CAPS- 5 as the criterion. Four hundred and five male and female Veterans who are primary care patients and are due for PTSD screening will complete the PC-PTSD-5 and will be interviewed by postdoctoral fellows using the CAPS-5. The study will determine the optimal cutoff for the PC-PTSD-5, explore the extent to which the optimal PC-PTSD-5 cutoff score varies across different Veteran subgroups of interest, and provide initial information about the acceptability of the screen for patients. Study results will enhance Veterans? healthcare by ensuring that PTSD screening is performed according to current diagnostic criteria using state of the art screening methods.